Method of and apparatus for determining the magnetic characteristics of material



March 24, 1936. K- L, sco-r1' I METHOD oF AND APPARATUS ECR DETERMININC TRE MAGNETIC CHARACTERISTICS CE MATERIAL A Filed Jan. 1, `1930 2 sheets-sheet 1 March 24, 1936. K. L. sco'rT 2,035,248

METHOD OF AND APPARATUS FOR DETERMINING THE MAGNETIC CHARACTERISTICS lOF' MATERIAL Filed Jan. 1, 1930 2 Sheets-sheet 2 @4. l' milan 34 /aaba o '10 2a .rra 4a 5a sa 7a e0 9a lao llo /20 Isa/40 lmao Patented Mer. 24, 1936 l 2,035,248 l UNITED sTATEs PATENT OFFICE METHOD OF AND APPARATUS FOR DETER- MINING THE MAGNETIC CHARACTERIS- TICS OF MATERIAL Kenneth L. Scott, Western Springs, Ill., assignor to Western Electric Company, Incorporated, New York, N. Y., a corporation of New York Application January 1, 1930, Serial No. 417,839

11 Claims. (Cl. F75-183) This invention relates to a method of and an netic properties are to be compared. Laminated apparatus for determining the magnetic charmagnetic yokes I8 are provided for completing acteristics of material, and more particularly the magnetic circuits for the test specimens, to a method of and an apparatus especially and are disposed in close engagement with the adapted to the determining of the magnetic members I1 and hold in this position by clamps 5 characteristics of soft metal parts, such as re- I9 0r the like. lay cores. To bring about the visual indicating `means The primary object of this invention is to a cathode ray Oscillograph iS electrically conprovide a, method and an apparatus which is nected to the testing circuit. This connection l0 simple and efficient and which allows the magis brought about by an indicating circuit Which netic characteristics of a metallic part to be electrically connects a defiecting coil 2l t0 the readily and accurately determinedterminal I6 by a conductor 22, and a deflecting In accordance with one embodiment of the coil 23 to the exact center of the secondary invention a sine wave of alternating voltage is Coil i3 of the transformer II by a Conductor applied, to the primary of a transformer, the 24. Deecting plates 25 and 26 are disposed 15 secondary of which -is in closed circuit with upon each side 0f the Datn of the electron beam interconnected coils for receiving test and standin the oscillograph and are in electrical conard specimens of material of equal cross section, nection With an alternating source 0f current the common points of the coils being connected through conductors 2l and 28 respectively.

to the mid-point of the secondary through the Further detailed description of the oscllograpn 20 deflecting coils of a cathode ray oscillograph. is deemed unnecessary as it iS of a Well known Under such conditions equal flux densities exist art, and also since its structure details d0 not in the specimens at every instant of time and form a part of the present inventionthe differences in the magnetizing current con- Fifom the foregoing descriptioniof the various trol the oscillograph to produce patterns visu- Darts of the apparatus the operation thereof Wi11 25 any indicating the differences. inthe magnetic be more clearly understood. A source of altercharacteristics of the specimens, nating current energy, preferably of lower fre- Other objects will be apparent from the folquency than siXty cycles Der Second, is Supplied lowing detailed description when considered in to the testingvorcuit- Due to the midpoint c011- connection with the accompanying drawings,y nection of the transformer the test coils I4 and 3o wherein I5, which are exactly equal in size andshape Fig. 1 is a wiring diagram illustrating the and llaVe an equal number of turns, .Will have invention; exactly equal voltages impressed thereon.

Fig 2 is a diagrammatic illustration of' a Therefore, the flux densities in the cores of the cathode ray oscillograph as incorporated in the test coils; for example, the test Specimens or 35 invention; members II, will always be equal if their cross- Fig, 3 is a, perspective View of tesi-,ing coils sections are equal. This is a valuable feature and clamping means for holding magnetic Vof the invention as it provides that the comyokes in engagement with members to be tested, parison of magnetic proporties in the two speciand mens shall always be madeat equal flux densi- 40 Figs. 4, 5, 6 and 'z are iiiustretions of the tios- The flux densities in the two coros or graphical derivation from actual hysteresis loops members il may be varied simultaneously by 0f patterns which would `lproduced by the Varying the Voltage lmpleSSed Oli the lie-St COllS.` i apparatus This is accomplishedby the actuation lof the 'Ihe wiring diagram shown in Fig. 1 illustrates induction regulator '0- j Y' a testing circuit provided with an induction Consideration ofFg- 1Will slioW thatthe in#Ur 'y ,regulator I0 and a transformer II, the latter dicating circuit, vWhich is connected With the having a primary coil I2 and a secondary coil test circuit at the common terminal I6 of the i I3. Two test coils I4 and I5 which are similar test coils I4 and I5 and the exact centerl of the in size and shape and which have an equal secondary coil I3, will carry a current equal'toli() number of turns are disposed in the circuit the dilerence between the magnetizing currents and electrically connected to each other by a owing in the two test coils. If the cores or common terminal indicated at I 6. members I1 have identical magnetic properties, The coils I4 and I5 are adapted to receive no current 'will ow in this indicating circuit,

5 cores or members indicated at I1 whose magsince the i'lux densities in the members are with respect to the electron beam, the spot on 'the oscillograph will be given a deflection directly proportional to the diierence in magnetizing current proper to any two test specimens -placed in the test coils at any desired value of magnetic induction. In order to produce a pattern with recognizable features such as that indicated at 29, it is necessary that the oscillograph spot be simultaneously delected along a4 perpendicular axis by an amount proportional to the magnetic induction itself, while the oscillograph spot is deflected along the horizontal axis by the deflecting coils 2| and 23. This is accomplished by applying a sine wave of electromotive force to the deflecting plates 25 and 26. `If the voltage applied to an iron cored coil is sinusoidal the wave form of the ux in the core will be sinusoidal, provided the resistance drop in the coil is kept suiliciently low. Therefore, if the voltage impressed on the tes't coils 4 and I5 issinusoidal, this voltage can serve as a source of defiecting potential for the oscillograph, due tothe connection of the indicating circuit with the test coils, which will have the same wave form as the ux in the members Il.

If the alternating source of current is twophase, a deecting potential can be secured which will not only have the same wave form as the flux in the members I1 but which will be in time phase with it. If only a single-phase source of current is available, the deflecting potential will be of the proper wave form, but it will be ,ninety degrees out of phase with the flux. Useful patterns may be obtained, however, with either source of current, but the use of la two-phase source is preferable.

In Figs. 4 to 'l inclusive are graphically derived the oscillograph patterns, only half of each being shown enlarged, which the apparatus would produce automatically by the use of silicon steel cores of specimens in a strained and unstrained condition. In Fig. 4 fis illustrated the usual hysteresis loops, determined ballistically, of two silicon steel specimens in a strained and annealed condition, which are obtained by plotting maxwells per square centimeter as ordinates and magnetizing force as abscissae. Re-

garding Fig. 5 the curve 36 represents the time variation of flux density in the specimen, and

- is obtained by plotting maxwells per square centimeter as ordinates and electrical degrees as abscissae. Curves 3"k and 36, which have gilberts per centimeter as ordinates and electrical degrees as abscissae, are derived point by point from curves 34, 35 and 36 by following a perpendicular from a point on the horizontal axis of Fig. 5 to the intersection Vwith cur-ve 36, thence along a horizontal line to curve 34, representing the annealed steel, and curve 35 the -s'trained steel from which the corresponding magnetizing forces are read o and plotted above the starting point on the horizontal axis of Fig. 5, as points on curves 31 and 38.

Curve 4| of Fig. 6 is derived by plotting differences, enlarged, between the magnetizing force curves 31 and.l 38 with the same ordinate and abscissa units referred to in connection with Fig. 5. yIt is noted that thepeak in the curve 4| does. not necessarily coincide with the peak of curve 40, which, like curve 36, is a sine wave of ux density, and consequentlythe tip A of the pattern 32 of Fig. 7 which is plotted with maxwells per square centimeter as ordinates and ux density as abscissae, does not necessarily coincide with the topmost point B of the pattern. The pattern 32 is obtained by plotting the several values derived from the curves 40 and 4| along mutually perpendicular axes in Fig. 7. Curve 33 of Fig. 7 is the coun` terpart of curve 32 but displaced through a phase angle of "l due to the displacement of curve 39 of Fig. 6 through a corresponding angle and is` obtained in a manner similar to that described for curve 32. The curves 32 and 33 represent the patterns produced 4on the oscillograph. By examining curve 32 and noting the displacement of the point B from the vertical axis, the dierence in the permeabilities of the two test samples may be determined. The sign of this diierence will also be indicated by noting whether the pattern 32 is displaced to the right or left of the vertical axis. sible to ascertain whether the unknown test specimen or the standard specimen has the higher permeability. Similarly, the width of the pattern 32 at its intersection with the horizontal axis is proportional to the difference between the coercive forces of the two specimens. Thus an observer can tell which has the higher coercive force. l

Therefore, with patterns produced by the combined horizontal and vertical deilection of the electron beam in the oscillograph the magnetic This makes it poscharacteristics of the cores or members may be automatically rendered into visible form. The

\ intercept on the horizontal axis (Fig. 7) by the pattern 33 is proportional to the required differences in permeabilities whereas the displacement ofthe tip of the pattern 33 from the vertical axis is proportional to the dilference in coercive force in the cores.` This is the reverse of which is true for pattern 32.

In view of the fact that the component of the magnetizing current owing in the test coils, which is related to eddy'currents, is nearly equal in both coils, the diierences between the components will be small, and the elfect of eddy currents in the cores will be largely kept out of the oscillograph patterns. Since these currents in the test coils cancel one another as far as the deilecting coils are concerned, the test coils are substantially alike.

It has been thoroughly pointed out how the magnetic characteristics of materials may be determined by the specic embodiment of this invention, but, in addition, since it is well known that the magnetic characteristics of magnetizable materials are closely related to and can be finished parts'inay be detected. The process of doingthis is toK read from the patterns the differences in magnetic properties of the specimens inthe manner previously described for magnetic materials, and then interpret these differences in magnetic properties of the specimens in terms of the associated mechanical properties. For example, in general, the greater the mechanical hardness of a specimen, the lower is its mag'- netic permeability and the higher is its coercive force, so, of two specimens under test the jone having the lower permeability andhigher coercive force, as disclosed by the oscillograph pattern, will have the greater hardness.

Although a specific form of apparatus has been disclosed as exemplifying the embodimentof the invention, it is understood that other forms of apparatus might be used without departing from the spirit and scope of the present invention.

What is claimed is:

1. In an apparatus of the character described, a testing circuit comprising test coils connected in series for receiving in each coil a member to be tested, a transformer having a secondary coil in electrical connection with said test coils, an indicating circuit disposed in electrical connection with said secondary coil and said testcoils for deflecting a ray of an oscillograph for indicating proportionally the diierences in permeabilities in the members, and means for deflecting the ray for indicating proportionally the diierences in coercive force in the members whereby these characteristics of the members may be read directly.

2. A method of determining the magnetic characteristics of members of materials, which consists of disposing the members as'cores in like coils, inducing Vequal flux densities in the members by applying currents of equal voltage to said coils, and controlling an oscillograph by the differences in magnetizing currents passing through said coils.

3. A method of determining the mechanical charactertistics of members of materials, which consists of disposing the members as. cores in test coils connected together and in closed circuit with the secondary of a transformer, inducing equal ilux densities in the members by impressing a voltage-on the transformer, and controlling an oscillograph by the diierences in magnetizing currents passing through the test coils.

4. In a testing device, a transformer, a pair of test coils having an equal number of turns connected in 'series to the secondary of said transformer, a conductor connected to the midpoint of said secondary and to the junction of the test coils, and an indicating device associ- 'ated with said conductor responsive to the difference in magnetizing currents in the test coils.

5. In a testing device, a pair of test coils having an equal number of turns, means for impressing equal voltages on saidtest coils, and an indicating device responsive to the instantaneous differences in magnetizing currents in the test coils.

6. In a testing device, a pair of test coils having an equal number of turns, means for applying equal voltages to said coils includinig a common conductor between the two terminal leads of said coils and said voltage applying means whereby magnetizing currents will flow in the conductor in accordance with the differences between the characteristics of the material being tested and an indicating device associated with and responsive to the current in said.' conductor.

'7. In an apparatus for testing magnetic materials, a pair of test coils, means for applying equal voltages to the test'coils, and means responsive to the difference in the wave form of the magnetizing currents in said coils for indieating the difference in magnetic properties I materials inserted in said coils.

8. In an apparatus for testing magnetic materials, a pair of test coils, means for applying equal voltages to said test coils, a cathode ray device for producing a cathode ray, means responsive to the diierence in the Wave form of the magnetizing currents in said test coils for deflecting said ray along one axis, vand means for continuously moving said ray along a perpendicular axis to indicate the magnetic prop.

erties of materials inserted in said coils.V

9. In an apparatus for testing magnetic materials, a pair of test coils, means for applying equal voltages to said coils, and means for visually indicating the difference in the wave forms of the magnetizing currents. I

10. in an apparatus of the character described, a testing circuit comprising test coils for receiving members to be tested, a transformer having a secondary coil in electrical connection with said test coils, means associated with said transformer and test coils for maintaining the voltages appliedto the test coils equal, and means for indicating the diierence in the instantaneous values of the permeabilities of materials inserted in the test coils.

11. In an apparatus of the character described, a testing circuit comprising test coils for receivingl members to be tested, means for applying equal voltages to said coils, and means responsive to the magnetizing currents of said coils for indicating permeability at a selected instantaneous voltage.

KENNETH L. SCOTI'. 

